missing data in RTS-GMLC.json

Got the following error when I use the latest Egret:

/Users/chiang7/project/2025/PCM/egrets_folks/egret-tests/test_cases/RTS-GMLC.json
Traceback (most recent call last):
  File "/Users/chiang7/project/2025/PCM/egrets_folks/egret-tests/egret_driver.py", line 57, in <module>
    md_in = ModelData.read(json_file)
  File "/Users/chiang7/project/2025/PCM/egrets_folks/egret-int/egret/data/model_data.py", line 189, in read
    return cls(source=du._read_from_file(filename, file_type))
                      ~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^
  File "/Users/chiang7/project/2025/PCM/egrets_folks/egret-int/egret/data/data_utils.py", line 117, in _read_from_file
    data = create_model_data_dict(filename)
  File "/Users/chiang7/project/2025/PCM/egrets_folks/egret-int/egret/parsers/ctm_parser.py", line 157, in create_model_data_dict
    data = ctmdata_2_model_data_dict(ctm)
  File "/Users/chiang7/project/2025/PCM/egrets_folks/egret-int/egret/parsers/ctm_parser.py", line 104, in ctmdata_2_model_data_dict
    elements['generator'] = ctm_gen_to_md(ctm.network.gen, ctm.time_series_data,
                            ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                                          ctm.temporal_boundary.gen,
                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^
                                          system, elements)
                                          ^^^^^^^^^^^^^^^^^
  File "/Users/chiang7/project/2025/PCM/egrets_folks/egret-int/egret/parsers/ctm_parser.py", line 387, in ctm_gen_to_md
    tmp_boundary_uids = list((g.uid for g in ctm_temporal_boundary_gen))
                                             ^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: 'NoneType' object is not iterable

I believe some data is missing in this model.

@iaravena

Start with test_cases/RTS-GMLC.json and the traceback path in egret/parsers/ctm_parser.py, especially ctm_gen_to_md and the temporal_boundary.gen input. Determine which model data is absent and how the parser expects it to be represented. Done means RTS-GMLC.json loads through ModelData.read without the NoneType iteration error.